The exemplary embodiment relates to the imaging arts. It finds particular application and connection with air knife stripping systems for fuser assemblies and will be described with specific reference thereto.
In typical electrostatographic printing systems, for example, such as copy machines and laser beam printers, a marking engine includes a photoconductive insulating member, such as a photoreceptor belt or drum, which is charged to a uniform potential and therefore exposed to light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member, which corresponds to the image areas contained within the document which is to be reproduced. Therefore, the electrostatic latent image on the photoreceptive insulating surface is made visible by developing the image with a marking material. Generally, the marking material comprises toner particles adhering triboelectrically to carrier granules, which is often referred to simply as toner. The image signals are stored and are read out successfully to a marking engine for formation of images and transfer of the images to a print medium, such as, sheets of paper.
In order to provide a high quality of service, it is useful to provide an easy releasing surface for treatment of the fuser roll. Untreated, the toner has a tendency to stick to the elastomeric surface of the heated fuser member. This problem is very common in the cases of members which are made of materials with relatively high surface energies as compared to materials such as Teflon. In these instances, release fluids are often employed to effectively reduce the surface energy of the roll and aid in the release of the toner. Even with the addition of release fluids and or low surface energy materials, it is often desirable to physically strip the printing media sheets from the fused surface of the roll. There are a variety of stripping solutions that are known in the art. However, it is desirable to have a method of stripping which is non-contact. Contact methods, such as stripping fingers, often cause premature wear which eventually results in the costly replacements of fusing members. One common method of non-contact stripping is the use of air knives.
In air knife stripping, jets of air are directed towards the print media to separate the print media from the fusing surface. The jets are emitted from small holes, or orifices, in an elongate surface which extends adjacent to the fuser roll. This method places an extrusion, having orifices directed towards the rolls in close proximity to the fuser nip. When the air knife's plenum is pressurized at a pressure higher than ambient air, the air is forced through the orifices and the jets of air impinge on fuse member surface. As the leading edge of the paper to be stripped approaches the impinging jet, lift and drag forces cause the paper to peel from the surface of the fuse member. The air jets have a tendency to lower the surface temperature of the fuse roll adjacent the jet through forced convection. This results in uneven gloss across the print media. For this reason it is found to be useful to apply a short burst of air, just as the leading edge of the print media reaches the air knife. The use of the short burst of air minimizes cooling, therefore, increasing the quality of the printing job.
The mass flow rate emanating from the jets is an important parameter to stripping performance. Air pressure can be a major factor in determining the flow rate, however, a reading of air pressure cannot detect orifice blockage. As a fusing air knife ages, orifices can become clogged by molten toner or other obstructions. As the orifices become clogged, the flow from that orifice reduces, resulting in a poor stripping performance.
If the air knife system develops blockage from molten toner or other objects, a service call is often required to diagnose the problem. There is a need in the industry to correct this problem to allow for a method of diagnosing orifice blockage without requiring a service call.